In reply to David Gwyer.

There's a lot of reasons not to move to PHP 7 yet. Not all the kinks have been worked out. Any custom code or your theme may be incompatible with PHP. Many plugins are still incompatible with PHP 7. Unless some is using his/her site to run a business and have a substantial budget for maintenance, a normal publisher would be better off running PHP 5.6 for the next six months. But yes, everyone should move to PHP 5.6 now, the moderately well-heeled or people with a busy site should move to PHP 7 now and everyone else should follow in about six months.

PHP 7 makes a big performance difference on a busy site (in terms of server load). On a site with low traffic, it's no big deal whether its PHP 5.6 or 7. After the initial page load to cache, the performance is not that different. Of course if your site has mainly logged in users pulling uncached pages, then the advantage of PHP 7 is substantial.

Early adopters and scouts exist for a reason. To work out the bugs before the mainstream arrive.